In the past temper rolling fluids have generally contained a nitrite salt to inhibit corrosion and one or more organic amine compounds, for example triethanolamine, to serve as a secondary corrosion inhibitor, and to act as an ion complexant.
Such fluids suffer from a number of disadvantages, including:
1. A tendency to foam, with consequent problems during metal working.
2. A tendency to hygroscopicity resulting in a complaint known as "wet pack" in respect of coil or sheet packs of steel which manifests itself in an unsightly appearance of the steel surface and which is detrimental to paintability.
3. Complaints relating to welder tip life by users of the steel.
4. Significant problems in waste disposal and water treatment at rolling mills, caused by the inclusion in such fluids of amine compounds.
5. Because of the problems in pollution control which arise from previously used fluids, it has been practised to recirculate rolling fluids and this in turn has given rise to problems with corrosion inhibition, product cleanliness and degradation of the fluid.
It is an object of the present invention to provide a fluid the use of which avoids or at least ameliorates some or all of those problems. The present invention provides a rolling fluid which avoids most of the disadvantages previously described while having substantially similar or superior performance to known rolling fluids in most other respects. More particularly, compositions according to the present invention do not contain amines and after use are more acceptable for waste discharge into the environment either with or without waste treatment. The composition possesses a mild cleaning action and results in more effective cleaning of steel strip during temper rolling and less susceptibility to "wet pack" formation in comparison with previously used fluids, resulting in improved paintability of the steel surface. Composition according to the invention may be made suitable for use with steel intended for food grade application. Rolling fluids according to preferred embodiments are less susceptible to excessive foaming during use than previously used fluids and may be made at lower raw materials cost per unit volume and with lower waste discharge pollution loadings. The fluids may be applied at lower surface loadings than has been usual with fluids hitherto in use and inhibit corrosion in steel after unpacking when the steel is exposed to high humidity.